Proton Conducting Polymer

Membrane Comprised of

2-Acrylamido-2-

Methylpropanesulfonic Acid

ARL-TR-2731 May 2002

Charles W. Walker Jr.

Approved for public release; distribution unlimited.
The findings in this report are not to be construed as an

official Department of the Army position unless so

designated by other authorized documents.

Citation of manufacturer’s or trade names does not

constitute an official endorsement or approval of the use

thereof.

Destroy this report when it is no longer needed. Do not return it to

the originator.
ARL-TR-2731 May 2002

Army Research Laboratory

Proton Conducting Polymer

Membrane Comprised of

2-Acrylamido-2-

Methylpropanesulfonic Acid

Charles W. Walker Jr.

Sensors and Electron Devices Directorate

Approved for public release; distribution unlimited.
In order to identify a proton-conducting polymer membrane suitable for replacing Nafion 117 in

direct methanol fuel cells, we prepared a cross-linked copolymer of hydrophilic

2-acrylamido-2-methylpropanesulfonic acid (AMPS) and 2-hydroxyethyl methacrylate (HEMA).

Fumed silicas were also added in an attempt to increase the amount of water adsorbed by the

membrane and to enhance water retention. Hydrated copolymer membranes adsorbed significantly

more water than Nafion® 117, but were no better at retaining water during drying under ambient

conditions. Films composed of 4 percent AMPS–96 percent HEMA had a room temperature

proton conductivity of 0.029 S cm–1, which increased to 0.06 S cm–1 at 80 °C.

Abstract

ii
iii

Contents

Introduction .................................................................................................................................. 1

Approach ....................................................................................................................................... 1

Experimental ................................................................................................................................. 2

Results and Discussion ................................................................................................................. 3

Conclusions ................................................................................................................................... 9

References.................................................................................................................................... 10

Report Documentation Page ...................................................................................................... 13

Figures

1. AMPS-HEMA copolymer .............................................................................. 2

2. Water uptake as a function of relative humidity ...................................................... 5

3. Water adsorbed as a function of AMPS content ...................................................... 6

4. Water loss of hydrated films at ambient conditions over time .................................... 7

5. Water loss of hydrated films with and without fumed silica at ambient conditions over time 7

6. Ionic conductivity as a function of temperature ...................................................... 8

7. Ionic conductivity as a function of temperature for polymers with and without silica added 9

1

Introduction

Fuel cells are being considered as direct replacements for batteries in Army applications to power

soldier-portable devices, as power supplies for recharging batteries, power for silent watch and

remotely-placed sensors, and for use in robotics and electric vehicles. A fuel cell can provide

uninterrupted power so long as the fuel is continuously supplied. The process involves the

conversion of chemical energy (hydrogen and oxygen) directly to electricity, heat and water.

Polymer electrolyte membrane fuel cell (PEMFC) technology is favored as a man-portable

system because of its light weight, high power, low operating temperature and fast start-up.

Hydrogen is oxidized at the anode to produce electricity and hydrogen ions that migrate through

the polymer electrolyte membrane to the cathode. The hydrogen ions combine with oxygen that

is reduced at the cathode to produce water. Although the preferred fuel is hydrogen, difficulties

remain with its safe storage, transport and handling in an economical and light weight system.

An alternative to hydrogen gas is to reform liquid fuels (e.g. alcohols, gasoline, diesel fuel) or

compressed gases (e.g. butane, ammonia) to produce hydrogen. This adds system weight, complexity and cost.

Direct methanol fuel cells (DMFC) oxidize methanol fuel directly at the fuel cell anode (no

separate reforming process) to produce electricity and hydrogen ions. However, there is a loss in

performance with the present systems. Current technology uses Nafion 117 as the polymer

electrolyte membrane which conducts protons from the anode to the cathode as well as serving

as the barrier between these two electrodes. However, performance is less than desired and

requires two primary areas of improvement. First, methanol permeates the membrane to cause a

“chemical short” at the cathode, where it directly reacts with oxygen, thereby decreasing fuel

utilization and oxygen cathode performance. Secondly, by improving the proton conductivity of

the membrane, higher current densities could be realized which could further reduce the size and

weight of the fuel cell. Additionally, Nafion 117 is very expensive, so identifying a less costly

material would have significant impact on system cost. This research attempted to address these

limitations by exploring new polymer membrane compositions based on the monomer 2-

acrylamido-2-methylpropanesulfonic acid (AMPS).

Approach

The ionic conductivity of Nafion is due to the ionization of hydrated sulfonic acid groups that

result in solvated protons. Conductivity is generally reported to be in the range of 0.08 to 0.1 S

cm–1, but the extent of membrane hydration is a critical factor in determining conductivity.

Conductivity increases with water content, but at temperatures exceeding 100  ̊C it decreases as

water is lost. Although Nafion is the current state-of-the-art membrane used for PEM fuel cells, it

is extremely expensive. A less costly material with improved ionic conductivity and water retention has been pursued for several years. Nafion also permits methanol to permeate the membrane, thereby rendering it unsuitable for use in DMFC’s.
2

In the work reported here, inexpensive hydrophilic AMPS monomer was chosen as a possible

candidate for a new electrolyte membrane based on the sulfonic acid group in its chemical

structure and on published work where it was prepared as a proton-conductive gel used in

electrochromic devices [1-8]. It has also been used as the basis for a humidity sensor [9] and as a

lithium ion conducting polymer electrolyte in a lithium battery [10]. Conductivity of semi-solid

poly-AMPS was found to be higher than that of partially hydrated Nafion that was hydrated to 15

water molecules per sulfonic acid group [2]. By contrast, conductivity of poly-AMPS increases

with water content only until about 6 molecules per equivalent and then levels off [2]. This

suggests that this polymer may be more tolerant to fluctuations in water content and drying, and

might maintain an ionic conductivity greater than Nafion under conditions of low water content.

Because AMPS homopolymers will only produce gels, extensive crosslinking or introduction of

a copolymer is required. By choosing a suitable copolymer, and with crosslinking, it may also be

possible to control methanol permeability, permitting its use in DMFC’s.

Poly(2-hydroxyethyl methacrylate) (HEMA) was chosen as a copolymer (Figure 1) because it

produces a water-insoluble but water-swellable polymer. Although it is hydrophobic, it’s waterswellable character means water will not be excluded from the copolymer. In addition to preventing polymer solubility, HEMA will provide structural stability and rigidity which should also

reduce methanol permeability.

Cross linking also prevents dissolution of the polymer in solvent and also reduces or prevents

swelling, thereby also reducing methanol permeablility. Ethylene glycol dimethacrylate (EGDM)

was chosen as a crosslinking agent, anticipating that it would further stiffen the polymer.

Experimental

The general synthetic procedure, substantially similar to that of Giglia [4,5], is to prepare a

50:50:5 ml solution of methanol, ethanol, and water which is deaerated by bubbling nitrogen.

While continuously stirring and slowly bubbling nitrogen, the desired ratio of AMPS and HEMA

(Aldrich) is added with a total weight of approximately 7 to 7.6 g. Approximately 2.5 wt%

EGDM (Aldrich) is then added followed by 1.3 wt% AIBN (Aldrich) free radical initiator to

n

Y ( ( C

C = O

)

O

OH

CH2 CH )X

C = O

NH

C CH3

CH3

H3C

CH2

CH2

CH2

CH2

SO3H

Figure 1. AMPS-HEMA copolymer.
3

catalyze the polymerization reaction. After the solids are completely dissolved, the solution is

refluxed at 60  ̊C with stirring and slow bubbling of nitrogen for 8 to 13 hours, then cooled to

room temperature. The polymer is solution cast in a Teflon dish or on a Teflon-coated fiberglass

mat. Solvent is allowed to evaporate in a fume hood at room temperature for 1 to 3 days, then the

film is placed in a 70  ̊C dry air oven for more complete solvent removal and to initiate the

crosslinking reaction.

Additional polymer formulations were prepared to include Nafion, which was introduced as a

5% solution (Aldrich), to improve mechanical properties. Dimethyl formamide (DMF, Aldrich)

was used as a co-solvent to alter mechanical properties. In addition, untreated fumed silica

(Cabosil EH-5) was added in an attempt to increase water absorption and water retention. Fumed

silicas are hydrophilic with an ability to adsorb moisture that increases with surface area. The

BET surface area of EH-5 is 380 m2g–1.

Water adsorption studies were performed after drying 1 cm2 coupons of polymer film under

vacuum at 65-70 ̊ C. Coupons were weighed and suspended from the caps of vials with a nickel

screen holder attached to the cap. The vials were partially filled with solutions of LiCl which

created atmospheres of 15%, 35%, 50%, 75%, 90% and 100% relative humidity (RH). Coupons

were periodically weighed over a period of one to two weeks until a stable weight was obtained,

from which wt% water adsorbed was calculated with respect to each sample’s dry weight. Drying rate of fully hydrated films was also determined by following weight loss over time under

ambient laboratory conditions.

Ionic conductivity was determined by AC impedance measurements taken between 10 Hz and

100 kHz using a Solartron AC impedance system (1260 impedance analyzer, 1287 electrochemical interface, Zplot software). A four-point probe method was employed using a test fixture

designed and constructed at Case Western Reserve University [11]. Samples measuring 3 cm by

0.5 cm were first hydrated in deionized water before assembly in the test fixture. The conductivity cell was placed in a sealable container having electrical feedthroughs and containing a small

amount of water to maintain an atmosphere of 100% relative humidity. The container was placed

in a Tenney chamber to control temperature. Impedance measurements were taken at each temperature after equilibrating for a minimum of two hours.

Results and Discussion

Physical Characteristics. Solution cast polymer films were clear and transparent, but brittle in

the dry state. When hydrated, the films became flexible. If the content of AMPS is too great (e.g.,

50 wt%), hydration results in a soft gel which is easily broken apart, whereas an intact flexible

film results when using less than 10% AMPS. Films containing 10% AMPS were relatively

fragile when hydrated and were unable to withstand rough handling. Decreasing AMPS content

to 5% provided a more robust film but was still judged as a little “soft”. When AMPS content

was 4% or less, hydrated films were more rugged and easily handled. The dimensional change as

the polymer swells with hydration was measured to be approximately 16% for a 2% AMPS

copolymer. Films with 2% fumed silica added had similar physical characteristics as polymer

without silica. Addition of 5% silica resulted in an uneven film noticeably containing silica

particles.
4

Nafion solution was used as an additive to try to lend mechanical flexibility to the dry polymer. It

was introduced by two methods: incorporated with the monomers and refluxed in the synthetic

process, or added to the AMPS-HEMA copolymer after refluxing and just prior to casting.

Composition of the film prepared was 2% AMPS, 5% Nafion and 93% HEMA. In both cases, a

visible phase separation was observed in the cast film. The films were composed of two distinct

areas, a clear portion and an opaque, milky white portion. Physical properties, water adsorption,

drying rate, and ionic conductivity of this formulation were equivalent to the AMPS-HEMA

copolymer without Nafion (data not presented).

Another effort to alter the mechanical properties was through the use of dimethyl formamide

(DMF). A 2% AMPS – 98% HEMA polymer was prepared in the usual manner except that the

amounts of ethanol and methanol were halved, and the difference made up with DMF. Solution

cast films were clear and seemed as brittle as films prepared without DMF. However, when

immersed in water the film hydrated quickly but became cloudy in appearance and disintegrated

into small pieces when handled.

Water Adsorption. Proton conductivity depends on the ability of the membrane to remain

hydrated, especially as temperature increases. Two strategies to increase water content and retain

water were the use of the hydrophilic AMPS monomer and the inclusion of silica.

Nafion-silica hybrid membranes have shown decreased methanol uptake [12] and increased

water content at temperatures below 120  ̊C [13]. Other polymers such as poly(vinylidene fluoride-co-hexafluoropropylene) blended with styrene [14] showed increased conductivity with the

addition of silica. Stonehart and Watanabe also claim the use of silica with various polymers

including Nafion to increase water content and conductivity [15,16]. However, Miyake,

Wainright and Savinell [13] found conductivity of Nafion to decrease with the addition of silica.

We added untreated fumed silica (2 and 5 wt%) to polymer solutions prior to casting in hopes of

increasing water absorption and retention, anticipating enhanced conductivity by increasing

water content. Fumed silicas also have chain-forming tendencies which form 3-D branched chain

aggregates. This entanglement could enhance mechanical strength of the polymer, and in fact has

been used by others [10] to improve mechanical properties of gel electrolytes containing AMPS.

Figure 2 shows water adsorption of various AMPS-HEMA polymer formulations compared with

Nafion equilibrated one to two weeks at various relative humidities. At relative humidities of

75% and below, differences in adsorbed water are very small to negligible, and only a small

increase in water content occurs as relative humidity increases. Above 75% RH, adsorbed water

increases sharply with increasing content of AMPS as well as for the Nafion membrane, but the

AMPS copolymers adsorb significantly more water than Nafion. At 90% RH, 10% AMPS contained 23 wt% water, Nafion 14 wt%. At 100% RH and for immersed samples, increases in water

adsorption are even more dramatic, with 10% AMPS adsorbing 69-71 wt% water while Nafion

adsorption ranges from 22-25 wt%. Membranes immersed in liquid water adsorbed even more

water than those equilibrated in saturated water vapor.

The two apparent regions of water adsorption have previously been observed and explained for

Nafion and seem appropriate for the AMPS copolymers as well. In the region of little increase in

water content (<75% RH), uptake of water is involved in the solvation of the protons and sulfonate ions in the membrane [17,18]. In the region above 75% RH, water is involved in filling

the pores and swelling of the polymer [17,18]. Two explanations have been offered for differences in water content for membranes equilibrated with water vapor and with liquid water [18].
5

The first involves several experimental difficulties such as obtaining a truly saturated vapor

phase. The second is that adsorption from the vapor phase involves condensation of water on the

hydrophobic surfaces of the polymer, which is less favorable than imbibing liquid water.

Comparison of water adsorption for a 4% AMPS copolymer with and without 2% silica shows

similar water uptake, with the silica-containing polymer adsorbing about 1 to 1.5 wt% more

water. There is one exception at 100% RH, where the silica-containing film adsorbs significantly

less water, but again exceeds the “plain” films in water-adsorbing capacity when immersed. The

experiment was repeated several times to confirm this unexpected incongruity. No explanation

for this anomaly is offered.

Increasing the silica content to produce a 4% AMPS – 91% HEMA – 5% Silica membrane did

not improve water adsorption capacity. Actually, water adsorption was slightly less than films

containing 2% silica (not shown). The improvement seen by adding silica to Nafion may occur

because relatively little water is normally adsorbed, so silica is effective in increasing the total

amount of adsorbed water. In contrast, high levels of water are already adsorbed by AMPS

copolymers without silica, so silica does not help to increase the overall uptake of water. Therefore, adding silica to the AMPS-HEMA copolymer offers no benefit, and effectively reduces the

ability of the films to adsorb water.

A plot of adsorbed water as a function of percent AMPS contained in the copolymer is shown in

Figure 3. We expected water uptake to increase with increasing wt% of AMPS in the copolymer,

but a maximum occurs for membranes containing only 4% AMPS either immersed in water or

equilibrated at 100% RH. We can only speculate on an explanation for this observation, but it

suggests that this composition should show the highest proton conductivity because of its higher

water content.

Loss of Adsorbed Water. Because AMPS is hydrophilic and HEMA is water swellable, we

hoped that the polymer would resist drying or at least dry at a slower rate than Nafion 117. The

addition of silica was also used in hopes of improving water uptake and retention. To determine

how well adsorbed water was retained, samples of AMPS-HEMA and Nafion were equilibrated

Figure 2. Water uptake as a function of relative humidity.

% Relative Humidity 

0 20 40 60 80 100

Immersed

0

20

40

60

80

100

0

20

40

60

80

100

10% AMPS - 90% HEMA 

5% AMPS - 95% HEMA

4% AMPS - 96% HEMA 

4% AMPS - 94% HEMA - 2% Silica

2% AMPS - 98% HEMA 

NAFION 117

Weight Percent Water Adsorbed
6

at 100% relative humidity or immersed in liquid water, then exposed to ambient conditions.

Weight loss was measured as a function of the total time samples were exposed to air. Immersed

samples initially retained more water than those equilibrated at 100% RH. However, after two

hours the wt% adsorbed water was the same for both samples. Surprisingly, both Nafion and the

AMPS copolymer lost the bulk of their adsorbed water very quickly. Within fifteen minutes, over

50% of the adsorbed water was lost, and over 80% was lost within one hour for all but 5%

AMPS – 95% HEMA which retained slightly more water (Figure 4). Loss of water slows after

one hour, approaching a state of equilibrium. Films containing 5% AMPS retained more water

than films with 2% AMPS as we expected. In general, the various ratios of AMPS-HEMA copolymer retained less than 10% of the adsorbed water, while Nafion retained about 15%. However, because AMPS copolymers adsorbed much more water than Nafion, the wt% water remaining is equal to or greater than that of Nafion.

The addition of 2% silica with 4% AMPS showed a similar rate of water loss as compared to

films containing 4% AMPS without silica. Actually, films with silica lost water at a slightly

faster rate than those without silica (Figure 5), which is counter to what we predicted especially

since adsorbed water increased by ~1.5% with the addition of silica. The drying rate data for 4%

AMPS with and without silica is essentially identical to that for 5% AMPS that had been immersed in water before drying. An increase in silica content to 5 wt% provided no benefit in

water retention. Membranes dried out as quickly as those containing 2 wt% silica, and overall,

lost slightly more water.

Ionic Conductivity. Based on the increased water content of the AMPS copolymers (compared

to Nafion) in saturated water vapor, we anticipated ionic conductivity to be high, perhaps exceeding that of Nafion. Conductivity was measured by the four-point probe method with a test fixture

designed and constructed by Case Western Reserve University [11]. At 100% RH and room

temperature, conductivity of Nafion 117 measured between 0.08 S cm–1 and 0.09 S cm–1, comparable to results published by others [19–22].

Figure 3. Water adsorbed as a function of AMPS content.

Weight Percent AMPS

02468 10 12

Weight Percent Adsorbed Water

40

50

60

70

80

90

Equilibrated at 100% RH

Immersed

+2% Silica

+2% Silica
7

AMPS-HEMA copolymer films containing 10% AMPS were too soft when hydrated to allow

rough handling, as were 5% films although to a lesser extent. Consequently, films had to be

handled carefully to prevent tearing, and impedance measurements were difficult since the

voltage-measuring pins of the conductivity cell could easily penetrate/puncture the films if too

much pressure was applied. A few impedance measurements of the 10% AMPS – 90% HEMA

films showed conductivity to be nearly equal that of the Nafion 117 polymer. Because of the

difficulty in handling, measurements of 5% and 10% AMPS-containing films were not thoroughly investigated.

Figure 4. Water loss of hydrated films at ambient conditions over time.

Figure 5. Water loss of hydrated films with and without fumed silica at

ambient conditions over time.

Time Exposed to Ambient Air / h

0 2 4 6 8 20

0

20

40

60

80

0

20

40

60

80

NAFION 117 100% RH

NAFION 117 Immersed

2% AMPS - 98% HEMA 100% RH

2% AMPS - 98% HEMA Immersed

5% AMPS - 95% HEMA 100% RH

5% AMPS - 95% HEMA Immersed

Weight Percent Adsorbed Water

Time Exposed to Ambient Air / h

0 1 2345678

0

10

20

30

40

50

60

90

100

0

10

20

30

40

50

60

90

100

4% AMPS - 96% HEMA

4% AMPS - 94% HEMA - 2% Silica

Weight Percent Adsorbed Water
8

Conductivity as a function of temperature for Nafion 117, 2% AMPS – 98% HEMA, and 4%

AMPS – 96% HEMA are compared in Figure 6. The conductivity of Nafion 117 is fairly constant with temperature, showing only a slight increase with temperature from ambient to 80  ̊C.

Conductivity at 23  ̊C was 0.076 S cm–1, increasing to 0.160 S cm–1 at 80  ̊C. Conductivity of

films containing 2% AMPS was about 500 times lower, measuring 1.55 × 10–4 S cm–1 at room

temperature, but showed a significant increase with temperature, reaching 1.6 × 10–3 S cm–1 at

80  ̊C.

Doubling the AMPS content to 4% increased the ionic conductivity considerably, to

0.029 S cm–1 at room temperature and 0.06 S cm–1 at 80  ̊C. Like Nafion, there is only a slight

increase in conductivity with increasing temperature. Considering the physical characteristics

associated with various levels of AMPS, 4% AMPS is the maximum level that provides an easily

handled hydrated membrane, and provides the best conductivity we can expect from a copolymer

film containing only these two polymers. Consequently, we must rely on other additives (e.g.

Nafion, silica) or additional copolymers (not included in this report) to improve ionic conductivity and physical characteristics.

As discussed earlier, addition of 5% Nafion with 2% AMPS – 93% HEMA was used to try to

improve film flexibility, but resulted in a phase separation between the Nafion and the AMPSHEMA. Conductvity of these films was identical to that measured for 2% AMPS – 98% HEMA

films.

Silica was added in an attempt to increase water adsorption and retention with the ultimate intent

of improving conductivity. Silica itself has been shown to be a proton conductor, with conductivity increasing with temperature and relative humidity [23]. Nafion-silica hybrid membranes have

shown decreased methanol uptake [12] and increased water content at temperatures below 120

 ̊C [13]. However, proton conductivity decreased as silica content in the Nafion was increased

[13]. We prepared AMPS-HEMA copolymers fixed at 4% AMPS and also containing 2% and 5%

fumed silica. Conductivity as a function of temperature is shown in Figure 7. Contrary to our

expectations, conductivity of film with 2% silica exhibits significantly lower conductivity than

Figure 6. Ionic conductivity as a function of temperature. Conductivity / S cm–1

10–4

10–3

10–2

10–1

100

Temperature / °C

10 20 30 40 50 60 70 80 90

Nafion 117

2% AMPS - 98% HEMA 

4% AMPS - 96% HEMA
9

film without silica added. Increasing silica content to 5% further decreased conductivity. Possible

explanations are that silica is blocking ion-conducting pathways and slowing ion movement by

causing ions to travel around silica particles, or that the silica is restricting the ability of the

membrane to swell and impedes diffusion of water. Unlike copolymer without silica, conductivity increases dramatically with increasing temperature. However, rather than a linear increase as

seen with the other films, the silica-containing membranes exhibit a break somewhere between

40  ̊C and 55  ̊C where conductivity increases sharply and then continues linearly. This suggests

that some activation energy is exceeded above 50  ̊C.

Conclusions

In our search for a less expensive alternative to Nafion, AMPS-HEMA copolymers and copolymers containing other additives were investigated to evaluate their possible use as protonconducting polymer membranes for use in fuel cells. AMPS was chosen based on the sulfonic

acid groups contained in its structure which are responsible for proton conductivity. HEMA was

chosen as a copolymer because it is water-insoluble and provides mechanical stability. Solution

cast films were found to be brittle when dry, so Nafion and dimethyl formamide were introduced

as additives to attempt to prepare more flexible films. These additions did not produce the intended result. Hydrated films were very pliable, but less rugged than Nafion 117. AMPS-HEMA

copolymer films with ≥ 5 wt% AMPS were too soft for rough handling when fully hydrated.

Compared to Nafion 117, water adsorption of AMPS-HEMA copolymer was dramatically improved at 100% relative humidity, and was greatest for compositions of 4% AMPS – 96%

HEMA. Water loss under ambient conditions was somewhat less for about an hour, but not

appreciably different than Nafion beyond two hours.

Figure 7. Ionic conductivity as a function of temperature for polymers with

and without silica added. Conductivity / S cm–1

10–3

10–2

10–1

100

Temperature / °C

10 20 30 40 50 60 70 80 90

Nafion 117

4% AMPS - 96% HEMA

4% AMPS - 94% HEMA - 2% Silica

4% AMPS - 91% HEMA - 5% Silica
10

Copolymers with only 2 wt% AMPS exhibited poor ionic conductivity. Increasing AMPS content

to 4 wt% greatly improved conductivity, which was slightly less than that of Nafion at temperatures between ambient and 80  ̊C. The 4% AMPS – 96% HEMA copolymer provides the highest

conductivity with reasonable mechanical integrity when hydrated to allow handling.

Attempting to increase the amount of adsorbed water, to retard membrane dry-out, and to increase ionic conductivity, fumed silicas were added to the copolymer. Water adsorption was not

enhanced, and loss of water under ambient conditions was comparable to copolymer without

silica. Ionic conductivity was actually worse, probably due to the silica particles interfering with

the ion-conducting pathways.

Although 4% AMPS – 96% HEMA copolymer was found to be a good ion conductor, improvements are still needed to be competitive with Nafion as a polymer electrolyte for a fuel cell.

Physical properties also need improving since in the dry state the polymer is too brittle for easy

handling and processing of membrane electrode assemblies. Other copolymers are being investigated to improve membrane flexibility and ionic conductivity, and to produce a film that is less

permeable to methanol than Nafion.

References

1. K. C. Ho, T. G. Rukavina, and C. B. Greenberg. J. Electrochem. Soc. 141 (1994) 2061.

Tungsten Oxide-Prussian blue Electrochromic System Based on a Proton-Conducting Polymer Electrolyte.

2. J. P. Randin. J. Electrochem. Soc. 129 (1982) 1215. Ion-Containing Polymers as Semisolid

Electrolytes in WO3-Based Electrochromic Devices.

3. J. M. Calvert, T. J. Manuccia, and R. J. Nowak. J. Electrochem. Soc. 133 (1986) 951. A

Polymeric Solid-State Electrochromic Cell.

4. R. D. Giglia, J. A. Sedlak, and D. W. Lipp. United States Patent 4,174,152, November 13,

1979. Electrochromic Devices with Polymeric Electrolytes.

5. R. D. Giglia and S. Y. Huang. United States Patent 4,375,318, March 1, 1983.

Electrochromic Cells with Improved Electrolye System.

6. S. Y. Huang and R. D. Giglia. United States Patent 4,478,991, October 23, 1984. Sulfonic

Acid Copolymer Electrolyte.

7. J. P. Randin. United States Patent 4,296,016, October 20, 1981. Method of Preparing a

Polymeric Electrolyte Particularly for an Electro-Optical Device.

8. M. C. Bernard, A.H.L. Goff, and W. Zeng. Electrochimica Acta 44 (1998) 781. Elaboration

and Study of a PANI/PAMPS/WO3 All Solid-State Electrochromic Device.

9. Y. Sakai, M. Matsuguchi, and N. Yonesato. Electrochimica Acta 46 (2001) 1509. Humidity

Sensor Based on Alkali Salts of poly(2-acrylamido-2-methylpropane sulfonic acid).
11

10. J. T. Sejdic, R. Steiner, J. Desilvestro, and P. Pickering. Electrochimica Acta 46 (2001) 1461.

Ion Conductivity of Novel Polyelectrolyte Gels for Secondary Lithium-Ion Polymer

Batteries.

11. B. D.Cahan and J. S. Wainright. J. Electrochem. Soc. 140 (1993) L185. AC Impedance

Investigations of Proton Conduction in Nafion.

12. N. Miyake, J. S. Wainright, and R. F Savinell. J. Electrochem. Soc. 148 (2001) A905. Evaluation of a Sol-Gel Derived Nafion/Silica Hybrid Membrane for Polymer Electrolyte Membrane Fuel Cell Applications. II. Methanol Uptake and Methanol Permeability.

13. N. Miyake, J. S. Wainright, and R. F Savinell. J. Electrochem. Soc. 148 (2001) A898. Evaluation of a Sol-Gel Derived Nafion/Silica Hybrid Membrane for Polymer Electrolyte Membrane Fuel Cell Applications. I. Proton Conductivity and Water Content.

14. H. Huang and S. L. Wunder. J. Electrochem. Soc. 148 (2001) A279. Ionic Conductivity of

Microporous PVDF-HFP/PS Polymer Blends.

15. P. Stonehart and M. Watanabe. United States Patent 5,523,181, June 4, 1996. Polymer SolidElectrolyte Composition and Electrochemical Cell Using the Composition.

16. M. Watanabe, H. Uchida, Y. Seki, and M. Emori. J. Electrochem. Soc. 143 (1996) 3847.

Self-Humidifying Polymer Electrolyte Membranes for Fuel Cells.

17. T. A. Zawodzinski, C. Derouin, S. Radzinski, R. J. Sherman, V. T. Smith, T. E. Springer, and

S. Gottesfeld. J. Electrochem. Soc. 140 (1993) 1041. Water Uptake by and Transport

Through Nafion 117 Membranes.

18. T. A. Zawodzinski, T. E. Springer, J. Davey, R. Jestael, C. Lopez, J. Valerio, and S.

Gottesfeld. J. Electrochem. Soc. 140 (1993) 1981. A Compative Study of Water Uptake By

and Transport Through Ionomeric Fuel Cell Membranes.

19. Y. Sone, P. Ekdunge, and D. Simonsson. J. Electrochem. Soc. 143 (1996) 1254. Proton

Conductivity of Nafion 117 as Measured by a Four-Electrode AC Impedance Method.

20. J.S.R. Samms, S. Wasmus, and R. F. Savinell. J. Electrochem. Soc. 143 (1996) 1498. Thermal Stability of Nafion in Simulated Fuel Cell Environments.

21. T. A. Zawodzinski, Jr., T. E. Springer, J. Davey, R. Jestel, C. Lopez, J. Valerio, and S.

Gottesfeld. J. Electrochem. Soc. 140 (1993) 1981. A Comparative Study of Water Uptake by

and Transport through Ionomeric Fuel Cell Membranes.

22. J. J. Sumner, S. E. Creager, J. J. Ma, and D. D. DesMarteau. J. Electrochem. Soc. 145 (1998)

107. Proton Conductivity in Nafion 117 and in a Novel Bis[(perfluoroalkyl)sulfonyl]imide

Ionomer Membrane.

23. F. M. Vichi, M. T. Colomer, and M. A. Anderson. Electrochem. and Solid-State Letters 2,

(1999) 313. Nanopore Ceramic Membranes as Novel Electrolytes for Proton Exchange

Membranes.

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NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102

Proton Conducting Polymer Membrane Comprised of

2-Acrylamido-2- Methylpropanesulfonic Acid

May 2002 Progress, Jan. 01 to Jan. 02

In order to identify a proton-conducting polymer membrane suitable for replacing Nafion 117

in direct methanol fuel cells, we prepared a cross-linked copolymer of hydrophilic

2-acrylamido-2-methylpropanesulfonic acid (AMPS) and 2-hydroxyethyl methacrylate

(HEMA). Fumed silicas were also added in an attempt to increase the amount of water adsorbed

by the membrane and to enhance water retention. Hydrated copolymer membranes adsorbed

significantly more water than Nafion® 117, but were no better at retaining water during drying

under ambient conditions. Films composed of 4 percent AMPS–96 percent HEMA had a room

temperature proton conductivity of 0.029 S cm–1, which increased to 0.06 S cm–1 at 80 °C.

2-acrylomido-2-methylpropanesulfonic acid, fuel cell, ion

conducting, polymer

Unclassified

ARL-TR-2731

2NENVV

611102.H47

AH47

61102A

ARL PR:

AMS code:

DA PR:

PE:

Approved for public release;

distribution unlimited.

17

Unclassified Unclassified UL

2800 Powder Mill Road

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U.S. Army Research Laboratory

Attn: AMSRL-SE-DC cwalker@arl.army.mil

U.S. Army Research Laboratory

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Charles W. Walker Jr.

email:

2800 Powder Mill Road

Adelphi, MD 20783-1197